ozone: drm: Allow importing buffers that cannot be added as framebuffers

After 6fc38604 ("ozone: drm: Move DrmFramebuffer from GbmBuffer to
GbmPixmap"), if a buffer's format is supported for scanout but cannot
be added as a framebuffer, we fail the import.

This broke CTS tests, so relax this test and add a note.

Bug: 872681
Test: ozone_unittests

Change-Id: I35e18f043abe21f5554369129da05448f990bfd4
Reviewed-on: https://chromium-review.googlesource.com/1169595
Commit-Queue: Michael Spang <spang@chromium.org>
Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582254}

ui/ozone/platform/drm/gpu/drm_framebuffer.cc

@@ -26,7 +26,7 @@ scoped_refptr<DrmFramebuffer> DrmFramebuffer::AddFramebuffer(
                                    params.handles, params.strides,
                                    params.offsets, modifiers, &framebuffer_id,
                                    params.flags)) {
-    PLOG(ERROR) << "AddFramebuffer2";
+    DPLOG(WARNING) << "AddFramebuffer2";
     return nullptr;
   }
 
@@ -38,7 +38,7 @@ scoped_refptr<DrmFramebuffer> DrmFramebuffer::AddFramebuffer(
                                    params.handles, params.strides,
                                    params.offsets, modifiers,
                                    &opaque_framebuffer_id, params.flags)) {
-    PLOG(ERROR) << "AddFramebuffer2";
+    DPLOG(WARNING) << "AddFramebuffer2";
     drm_device->RemoveFramebuffer(framebuffer_id);
     return nullptr;
   }

ui/ozone/platform/drm/gpu/drm_thread.cc

@@ -202,9 +202,9 @@ void DrmThread::CreateBufferFromFds(
 
   scoped_refptr<DrmFramebuffer> framebuffer;
   if (buffer->GetFlags() & GBM_BO_USE_SCANOUT) {
+    // NB: This is not required to succeed; framebuffers are added for
+    // imported buffers on a best effort basis.
     framebuffer = DrmFramebuffer::AddFramebuffer(drm, buffer.get());
-    if (!framebuffer)
-      return;
   }
 
   *out_buffer = std::move(buffer);